Integrated circuit chip manufacturers fabricate semiconductor devices by depositing, growing, and etching numerous layers of semiconductors, metals and insulating materials on a semiconductor wafer. Device processing involves placing the wafer within a processing reactor and exposing it to various process energy sources and reactive chemical compounds. The wafer processing equipment usually includes a process chamber in which the process energy sources affect the process environment and the semiconductor wafer. These process energy sources may include, for example, radio-frequency or microwave power sources for the generation of energetic metastables and ions in a process plasma, heat sources such as wafer heating lamps, and magnetron plasma sources. Another process energy or activation source that has numerous applications in low-temperature semiconductor device processing is ultraviolet (UV) light.
Nar, et al., "Photochemical Cleaning and Epitaxy of Si," SPIE Conference on Advances in Semiconductors and Semiconductor Structures, Dec. 21, 1988, describes a UV-assisted photochemical process for epitaxial growth of silicon. That paper presents reduced temperature processes for surface cleaning and epitaxial growth made possible by UV light irradiation of the process gases and semiconductor wafer surface. Through the use of UV irradiation, native oxide layers on silicon substrates can be removed at 730.degree. C. and epitaxial silicon layers with high crystal quality can be deposited at a temperature as low as 540.degree. C. in a disilane process ambient.
Both the photon energy (or light wavelength) spectrum and intensity of the deep UV energy source affect the kinetics or rate of a photochemical process. For a given set of process conditions, increasing the deep UV irradiation intensity also enhances the photochemical processing rate. The deep UV light sources used for photochemical device processing can be divided into two categories: broad-band sources with continuous and finite irradiation spectra, and narrow-band or monochromatic sources with distinct and well-defined (almost singlewavelength) emission lines. The deep UV light sources for photochemical processing usually operate at a single-wavelength or an irradiation band in the wavelength range of 100-400 nm. The photo enhancement of a deposition, etch, or surface cleaning process occurs either via photo-dissociation of a reactive process gas or photo enhancement of a surface-related process (reaction or desorption). The irradiation wavelength or spectrum must be optimized for a given process in order to effectively excite the gas molecules and/or activate the surface reaction/desorption. However, the photochemical processing systems proposed to date employ external UV sources, and are usually incompatible with other process energy sources such as a plasma. Moreover, most of these external and expensive light sources do not provide any wavelength tuning capabilities to optimize various photochemical processes.
Thus, there is a need for a method and apparatus that effectively and efficiently utilizes the advantages of ultraviolet light irradiation for semiconductor device fabrication and is compatible with additional process energy sources such as a plasma. Such a method may be used for removal of residual surface organic contaminants by ultraviolet/ozone cleaning, photochemical removal of metallic contaminants, photochemical etching, and low-temperature UV-assisted deposition applications.
Known methods of exposing a semiconductor wafer to UV photons require the use of an ex-situ deep ultraviolet energy source. The source emits deep ultraviolet photons, and irradiates the process environment and semiconductor wafer through a quartz window on the processing reactor. Several limitations are associated with the use of an external deep ultraviolet light source for semiconductor wafer photochemical processing. For example, an ex-situ deep ultraviolet photon source suitable for semiconductor wafer processing is rather expensive, takes up considerable space, and can limit the operational flexibility and ultimate throughput of a wafer production facility. Furthermore, the quartz window of the processing reactor attenuates the deep ultraviolet photon flux. Finally, formation of deposits on the quartz windows can further degrade UV light transmission and the photochemical process efficiency. Yet another drawback associated with the use of an ex-situ deep ultraviolet light source is that it consumes one available access port on the process chamber. As a result, the use of an external light source imposes a restriction on the process chamber design and implementation of any additional process energy sources such as a plasma. Moreover, process uniformity requirements in photochemical processing based on the use of external light sources usually impose a constraint on reactor and process chamber design. Optimum process uniformity typically requires that the semiconductor wafer be placed very close to the quartz window and the light source.
Thus, there is a need for an inexpensive ultraviolet photon source for efficient in-situ photochemical processing of semiconductor wafers.
There is a need for a deep ultraviolet photochemical energy source that does not occupy significant space in a wafer production facility.
There is a need for a deep UV photochemical energy source which provides capabilities for real-time adjustment and optimization of the UV irradiation spectrum and intensity.
Furthermore, there is a need for a deep UV photochemical process energy source that is fully compatible with existing plasma processing reactors and plasma process energy sources.